title: Women and men with hip fractures have a longer femoral neck moment arm and greater impact load in a sideways fall.
abstract: BACKGROUND
  In a case control study, we report that women and men with hip fractures have a longer moment arm of the force applied on the proximal femur during a sideways fall, a structural feature that may contribute to fracture risk. The impact load and its direction during a sideways fall onto the greater trochanter are partly determined by the geometry of the proximal femur. We hypothesized that the hip geometry in elderly with hip fractures produces a greater impact on the hip during a sideways fall.
  
  
  METHODS
  We studied 41 female (77.2 +/- 9.9 years) and 22 male (76.2 +/- 12.1 years) patients with hip fractures and 40 female (85.7 +/- 6.0 years) and 17 male (84.3 +/- 10.1 years) controls. Hip geometry was analyzed on the nonfracture hip in patients and left hip in controls using dual-energy X-ray absorptiometry.
  
  
  RESULTS
  There was no difference in areal bone mineral density (aBMD), hip axis length, femoral neck axis length, or neck-shaft angle between cases and controls. However, the moment arm of the force on the hip during a sideways fall was 7.3% and 9.5% longer resulting in 5.6% and 9.1% greater moment in such a fall in female and male cases relative to their respective controls independent of height and weight (all p < 0.056). In multivariate logistic regression analysis, only the moment arm length in a sideways fall was associated with increased risk of hip fracture in females (odds ratio = 1.91, 95%CI: 1.14-3.20 for each SD increase in moment arm length of sideways fall, p = 0.02) and males (odds ratio = 2.69, 95% CI, 1.19-6.09, p = 0.01).
  
  
  CONCLUSIONS
  A longer moment arm in the sideways fall increases the resultant force applied to the hip predisposing to hip fracture.
authors.affiliation: Endocrine Centre, Department of Medicine/Austin Health, The University of Melbourne, Victoria, Australia. Qingjuw@yahoo.com
authors.forename: Q
authors.initials: Q
authors.lastname: Wang
authors.forename: J W
authors.initials: JW
authors.lastname: Teo
authors.forename: A
authors.initials: A
authors.lastname: Ghasem-Zadeh
authors.forename: E
authors.initials: E
authors.lastname: Seeman
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D000058:Accidental Falls; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D015519:Bone Density; D001851:Bone Diseases, Metabolic / Q000453:epidemiology; D016022:Case-Control Studies; D005260:Female; D005269:Femur / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D005272:Femur Neck / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D006620:Hip Fractures / Q000209:etiology / Q000473:pathology*; D006621:Hip Joint / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D006801:Humans; D008297:Male; D008875:Middle Aged; D010024:Osteoporosis / Q000453:epidemiology; D010384:Pelvic Bones / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D011312:Pressure / Q000009:adverse effects; D012307:Risk Factors; D013314:Stress, Mechanical; D014739:Victoria / Q000453:epidemiology